Polycarbonate coated with photocurable polythiol and different polyenes

ABSTRACT

A photocurable composition suitable for coatings comprising a polythiol and two different polyenes. These coating compositions are suitable for coating polycarbonate articles.

This invention is directed to a photocurable composition suitable forcoatings comprising a polythiol, and two different polyenes. Thesecoating compositions are suitable for coating polycarbonate articles.

BACKGROUND OF THE INVENTION

Commercial liquid coating compositions are available. Many of thesecoating compositions are not suitable for coating polycarbonate articlessince they are not compatible with the polycarbonate. Also, the uncuredcoating may adversely affect the polycarbonate article by stresscracking and crazing it, by causing crack propogation into thepolycarbonate as a result of brittleness of the coating itself and/or byreducing the properties of the polymer generally such as, for example,impact resistance, elongation, tensile strength and so on. Further,several coatings while compatible with the polycarbonate have little orno chemical barrier properties and/or poor adhesion.

Therefore, a successful coating for polycarbonate articles must becompatible with the polycarbonate and provide barrier or other desirablesurface properties while maintaining mechanical or other properties ofthe polymer substrate and themselves provide chemically resistantsurfaces. Also, the cured coating, in this particular application,should particularly provide the coated polycarbonate article withanti-skid properties in addition to the chemical barrier propertiesnecessary to prevent crazing of the substrate polycarbonate inchemically aggressive environments.

DESCRIPTION OF THE INVENTION

The instant invention is concerned with a photocurable compositionsuitable for coating polycarbonate articles comprising a polythiol andtwo different polyenes. These coating compositions are especiallysuitable for coating polycarbonates. Upon curing, the coatings provide apolycarbonate article with anti-skid properties, chemical resistance,scratch resistance and chemical barrier properties resulting instress-crazing resistance. Also, the coating composition of the instantinvention allows the polycarbonate substrate to retain its inherentdesirable physical properties (particularly impact resistance) by whichit is distinguished.

The photocurable coating composition comprises:

(a) a polythiol of the general formula: ##STR1## WHEREIN R₁ and R₂ areorganic moieties containing no reactive carbon-to-carbon unsaturationand a is 2 to 4;

(b) a polyene of the general formula: ##STR2## WHEREIN R₃ and R₄ areorganic moieties containing no reactive carbon-to-carbon unsaturationand b is 2 or greater; and

(c) a polyene of the general formula: ##STR3## WHEREIN R₆ and R₇ areorganic moieties containing no reactive carbon-to-carbon unsaturationand c is 1 or greater, and wherein (a) and (b) plus

(c) are used in stoichiometric amounts.

The polythiols of (a) are prepared by reacting an ester of thiolcontaining acids of the formula HS--R₂ --COOH wherein R₂ is an organicmoiety containing no reactive carbon-to-carbon unsaturation, withpolyhydroxy compounds of structure R₁ (OH)_(a) wherein R₁ is an organicmoiety containing no reactive carbon-to-carbon unsaturation and a is 2to 4. These components react under conditions known in the art and asare set forth in U.S. Pat. No. 3,661,744, which is incorporated hereinby reference. Preferably, the polythiol of (a) has the following generalformula: ##STR4## wherein R₁ and R₂ are straight chain aliphaticmoieties containing no reactive carbon-to-carbon unsaturation and a is 2to 4.

The polyenes of (b) and (c) are prepared by methods known in the art andas set forth in U.S. Pat. No. 3,661,744, which is incorporated herein byreference. Preferred polyenes of type (b) have the following generalformula: ##STR5## wherein R₃ and b are as defined above.

Most preferably, the polyenes of (b) are oligomer of diallyl phthalatehaving residual unsaturation of the type represented by the generalformula: ##STR6## wherein R₇ is an organic moiety derived from diallylphthalate by oligomerization and b is an integer of 2 or greater.

The polyenes of (c) preferably have the following general formula:##STR7## wherein R₆ and R₇ are defined as above.

Most preferably, the polyenes of (c) are of the formula: ##STR8##wherein R₆ is as defined above and has a molecular weight of about1,000.

The photocurable composition is a liquid polymer and may be formulatedfor use as 100 percent solids, or disposed in organic solvents, or asdispersions or emulsions in aqueous media, prior to curing.

The curable liquid polymer compositions prior to curing may readily bepumped, poured, siphoned, brushed, sprayed, doctored, or otherwisehandled as desired. Following application, curing in place to thepolycarbonate article may be effected either very rapidly or extremelyslowly as desired by manipulation of the compounding ingredients and themethod of curing.

The curing reaction may be initiated by most actinic light sources thatdisassociate or abstract a hydrogen atom from an SH group, or accomplishthe equivalent thereof. Generally, the rate of the curing reaction maybe increased by increasing the temperature of the composition at thetime of initiation of cure. In many applications, however, the curing isaccomplished conveniently and economically by operating at ordinary roomtemperature conditions.

By proper choice of type and concentration of photocuring rateaccelerator for initiation, the curing period required for conversion ofthe polythiol-polyenes composition from the liquid to the solid statemay be varied greatly as desired. In combination with suitableaccelerators or retarders, the curing period may vary from about asecond or less to about 30 days or more. In general, short curingperiods are achieved in applications where thin films of curablecompositions are required, such as in the field of coatings whereas thelong curing periods are achieved and desired where more massive layersor composition are required, such as in the field of elastomericsealants.

A class of actinic light useful herein is ultraviolet light and otherforms of actinic radiation which are normally found in radiation emittedfrom the sun or from artificial sources such as Type RS Sunlamps, carbonarc lamps, xenon arc lamps, mercury vapor lamps, tungsten halide lampsand the like. Ultraviolet radiation may be used most efficiently if thephotocurable coating composition contains a suitable photocuring rateaccelerator. Curing periods may be adjusted to be very short and hencecommercially economical by proper choice of ultraviolet source,photocuring rate accelerator and concentration thereof, temperature andmolecular weight, and reactive group functionality of the polyene andpolythiol.

Conventional curing inhibitors or retarders which may be used in orderto stabilize the components or curable compositions so as to preventpremature onset of curing may include hydroquinone; p-tert-butylcatechol; 2,6-di tert-butyl-p-methylphenol; phenothiazine;N-phenyl-2-naphthylamine; inert gas atmosphere such as helium, argon,nitrogen and carbon dioxide; vacuum; and the like.

It is understood to be within the scope of this invention that thephotocuring rate accelerator may be present as a separate and distinctcomponent such as azobenzene, as a mixture of two or more separatecomponents, such as benzophenone; benzanthrone; anthrone anddibenzosuberone; carbon tetrachloride and phenanthrene; and the like, orin chemically combined form within the molecular structure of either thepolyenes or the polythiol. An example of this latter condition whereinthe photocuring rate accelerator is present not as a separate component,but rather in a form chemically combined within the polyene component isthe following structure which contains four reactive carbon-to-carbonunsaturated groupings and one diaryl ketone grouping per averagemolecule: ##STR9##

It is further understood that the polyenes, the polythiol or thephotocuring rate accelerator may be formed in situ in the photocurablecomposition without departing from the spirit of this invention.

Specifically useful herein are chemical photocuring rate acceleratorssuch as benzophenone, acetophenone, acenaphthenequinone, o-methyoxybenzophenone, thioxanthen-9-one, xanthen-9-one,7-H-Benz(de)anthracen-7-one, dibenzosuberone, 1-napththaldehyde,4,4'-bis (dimethylamino) benzophenone, fluorene-9-one,1'-acetonaphthane, anthraquinone, 1-indanone, 2-tert-butylanthraquinone, valerophenone, hexanophenone, 3-phenyl-butyrophenone,p-morpholinopropiophenone, 4-morpholino-benzophenone, p-diacetylbenzene,4-amino-benzophenone, 4'-methoxyacetophenone, benzaldhyde, α-tetralone,9-acetylphenanthrene, 2-acetylphenanthrone, 10-thioxanthenone,3-acetylphenanthrene, 3-acetylindole, 1,3,5-triacetylbenzene and thelike, including blends thereof, to greatly reduce the exposure times.

The curing rate accelerators are usually added in an amount ranging fromabout 0.005 to about 50 percent by weight of the photocurablecomposition, with a preferred range being from about 0.05 to about 25percent by weight. Preferred photocuring rate accelerators are thealdehyde and ketone carbonyl compounds having at least one aromaticnucleus attached directly to the ##STR10## group.

The compositions to be cured, i.e., (converted to solid resins orelastomers) in accord with the present invention may, if desired,include such additives as antioxidants, accelerators, dyes, inhibitors,activators, fillers, pigments, antistatic agents, flame-retardantagents, thickeners, thixotropic agents, surface-active agents, viscositymodifiers, extending oils, plasticizers, tackifiers and the like withinthe scope of this invention. Such additives are usually preblended withthe polyene or polythiol prior to or during the compounding step.Operable fillers include natural and synthetic resins, carbon black,glass fibers, wood flour, clay, silica, alumina, carbonates, oxides,hydroxides, silicates, glass flakes, glass beads, borates, phosphates,diatomaceous earth, talc, kaolin, barium sulfate, calcium sulfate,calcium carbonate, antimony oxide and the like. The aforesaid additivesmay be present in quantities up to 500 parts or more per 100 partspolymer by weight and preferably about 0.0005 to about 300 parts on thesame basis.

A useful method of compounding is to prepare in an ambient atmosphere byconventional mixing techniques but in the absence of actinic radiation acomposition consisting of polyenes, antioxidant (to inhibit spontaneousoxygen-initiated curing), polythiol, UV sensitizer of photoinitiator,and other inert additives. This composition may be stored in the darkfor extended periods of time, but on exposure to actinic radiation(e.g., ultraviolet light, sunlight, etc.) will cure controllably and ina very short time period to solid polythioether products.

The coating composition of the instant invention may be applied to thepolycarbonate surface by any conventional coating technique such asroll, curtain or spray.

In the practice of this invention, any of the aromatic polycarbonatescan be employed herein. These are homopolymers and copolymers andmixtures thereof that are prepared by reacting a dihydric phenol with acarbonate precursor. Typical of some of the dihydric phenols that may beemployed in the practice of this invention are bisphenol-A,2,2-bis(4-hydroxyphenyl) propane), bis (4-hydroxyphenyl) methane,2,2-bis(4-hydroxy-3-methylphenyl) propane, 4,4-bis(4-hydroxyphenyl)heptane, 2,2-(3,5,3',5'-tetrachloro-4,4'-dihydroxydiphenyl) propane,2,2-(3,5,3',5'-tetrabromo-4,4'-dihydroxydiphenyl) propane,(3,3'-dichloro-4,4'-dihydroxyphenyl) methane. Other dihydric phenols ofthe bisphenol type are also available and are disclosed in U.S. Pat.Nos. 2,999,835, 3,028,365 and 3,334,154.

It is, of course, possible to employ two or more different dihydricphenols or a copolymer of a dihydric phenol with a glycol or withhydroxy or acid terminated polyester, or with a dibasic acid in theevent a carbonate copolymer or interpolymer rather than a homopolymer isdesired for use in the preparation of the aromatic carbonate polymers ofthis invention. Also employed in the practice of this invention may beblends of any of the above materials to provide the aromatic carbonatepolymer.

The carbonate precursor may be either a carbonyl halide, a carbonateester of a haloformate. The carbonyl halides which can be employedherein are carbonyl bromide, carbonyl chloride and mixtures thereof.Typical of the carbonate esters which may be employed herein arediphenyl carbonate, di-(halophenyl) carbonates such as di-(chlorophenyl)carbonate, di-(bromophenyl) carbonate, di-(trichlorophenyl) carbonate,di-(tribromophenyl) carbonate, etc., di-(alkylphenyl) carbonate such asdi(tolyl) carbonate, etc., di-(naphthyl) carbonate, di-(chloronaphthyl)carbonate, phenyl tolyl carbonate, chlorophenyl chloronaphthylcarbonate, etc., or mixtures thereof. The haloformates suitable for useherein include bis-haloformates of dihydric phenols (bischloroformatesof hydroquinone, etc.) or glycols (bishaloformates of ethylene glycol,neopentyl glycol, polyethylene glycol, etc.). While other carbonateprecursors will occur to those skilled in the art, carbonyl chloride,also known as phosgene, is preferred.

Also included are the polymeric derivatives of a dihydric phenol, adicarboxylic acid and carbonic acid. These are disclosed in U.S. Pat.No. 3,169,121 which is incorporated herein by reference.

The aromatic carbonate polymers of this invention may be prepared byemploying a molecular weight regulator, an acid acceptor and a catalyst.The molecular weight regulators which can be employed in carrying outthe process of this invention include monohydric phenols such as phenol,chroman-T, paratertiarybutylphenol, parabromophenol, primary andsecondary amines, etc. Preferably, phenol is employed as the molecularweight regulator.

A suitable acid acceptor may be either an organic or an inorganic acidacceptor. A suitable organic acid acceptor is a tertiary amine andincludes such materials as pyridine, triethylamine, dimethylaniline,tributylamine, etc. The inorganic acid acceptor may be one which can beeither a hydroxide, a carbonate, a bicarbonate, or a phosphate of analkali or alkaline earth metal.

The catalysts which are employed herein can be any of the suitablecatalysts that aid the polymerization of bisphenol-A with phosgene.Suitable catalysts include tertiary amines such as for example,triethylamine, tripropylamine, N,N-dimethylaniline, quaternary ammoniumcompounds such as, for example, tetraethylammonium bromide, xetyltriethyl ammonium bromide, tetra-n-heptylammonium iodide, tetra-n-propylammonium bromide, tetramethylammonium chloride, tetramethyl ammoniumhydroxide, tetra-n-butylammonium iodide, benzyltrimethylammoniumchloride and quaternary phosphonium compounds such as for example,n-butyltriphenyl phosphonium bromide and methyltriphenyl phosphoniumbromide.

Also, included herein are branched polycarbonates wherein apolyfunctional aromatic compound is reacted with the dihydric phenol andcarbonate precursor to provide a thermoplastic randomly branchedpolycarbonate.

These polyfunctional aromatic compounds contain at least threefunctional groups which are carboxyl, carboxylic anhydride, haloformylor mixtures thereof. Examples of these polyfunctional aromatic compoundswhich may be employed in the practice of this invention include:trimellitic anhydride, trimellitic acid, trimellityl trichloride,4-chloroformyl phthalic anhydride, pyromellitic acid, pyromelliticdianhydride, mellitic acid, mellitic anhydride, trimesic acid,benzophenonetetracarboxylic acid, benzophenonetetracarboxylic anhydrideand the like. The preferred polyfunctional aromatic compounds aretrimellitic anhydride or trimellitic acid, or their haloformylderivatives.

Also, included herein are blends of a linear polycarbonate and abranched polycarbonate.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following examples are set forth to illustrate more clearly theprinciple and practice of this invention to those skilled in the art.Unless otherwise specified, where parts or percents are mentioned, theyare parts or percents by weight.

EXAMPLE I

A sample of polycarbonate of 2,2'-bis-(4-hydroxyphenyl) propane havingan intrinsic viscosity of 0.57 deciliters is molded into test specimensof 4 inch × 4 inch × 1/4 inch and tested for toughness andstress-crazing.

The toughness of the specimen is determined by moving the fingernails ofa hand back and forth across the test specimen with medium pressure andobserving whether or not the coating scratches.

The stress-crazing of the 4 inch × 4 inch specimen is determined byplacing it on a material, such as an equivalent size of carpet, placinga steel ball in the center of the combination and applying a load plateof 100 lbs. to the steel ball. The sample is allowed to remain understress for 7 days. The sample of polycarbonate is then examined aroundthe stress point for any sign of stress crazing.

The polycarbonate of this example is molded into a test specimen of 10inch × 10 inch × 1/4 inch and tested for its anti-skid properties. Theanti-skid rating is determined by placing three 7/8 inch diameter steelballs, welded together to form a triangle, on the test specimen andraising one end of the specimen vertically while keeping the oppositeend on the horizontal plane. The distance in inches to which the edge israised vertically when the weight slides down the sample is recorded. Avalue of 7-8 is considered acceptable.

The test results are summarized in Table I.

EXAMPLE II

Sheets of 4 inch × 4 inch × 1/4 inch and 10 inch × 10 inch × 1/4 inch,made from the polycarbonate of Example I, were coated with a coatingwhich is a mixture of a stoichiometric amount of a thiol of the formula:##STR11## and a polyene of the formula: ##STR12## in a thickness in therange of 0.5 mils to 2.5 mils and cured with ultraviolet light for 60seconds. The coated sheets were tested as described in Example I andalso tested for coating adhesion.

The coated adhesion is measured on the coated sheet with scotch tape. Inthe unscribed coating adhesion test, a strip of scotch tape is appliedto the surface of the coating, taking care to hold one end of the stripaway from the surface. The tape is removed rapidly by pulling the freeend at a 90° angle away from the surface. Removal of the coating withthe tape is considered adhesion failure. In the scribed coating adhesiontest, the coating surface is scribed with a sharp instrument such as arazor blade or a Gardner cross-cut (lattice cutting) tester. The scribedarea consists of two sets of parallel scribes 1-2 mm. apart,perpendicular to each other. The scotch tape is applied (as above) overthe scribed area and removed in the same manner as above. The coating isthen examined for partial or complete removal of the squares or nochange.

EXAMPLE III

Sheets of 4 inch × 4 inch × 1/4 inch and 10 inch × 10 inch × 1/4 inchmade from polycarbonate of Example I, were coated with a coating whichis a mixture of a stoichiometric amount of the thiol of Example II and apolyene of the formula: ##STR13## where n is an integer wherein themolecular weight is equal to 1000, in a thickness in the range of 0.5mils to 2.5 mils and cured with ultraviolet light for 60 seconds. Thecoated sheets were tested as described in Examples I and II. The resultsare set forth in Table I.

EXAMPLE IV

Sheets of 4 inch × 4 inch × 1/4 inch and 10 inch × 10 inch × 1/4 inchmade from the polycarbonate of Example I were coated with a coatingwhich is a mixture of a stoichiometric amount of the thiol of Example IIand a stoichiometric amount of the combination of a polyene of theformula: ##STR14## and a polyene of the formula: ##STR15## where n is aninteger wherein the molecular weight is equal to 1000, in a thickness inthe range of 0.5 mils to 2.5 mils and cured with ultraviolet light for60 seconds. The coated sheets were tested as described in Examples I andII. The results are set forth in Table I.

                  Table I                                                         ______________________________________                                               Example 1                                                                             Example 2 Example 3 Example 4                                  ______________________________________                                        Toughness                                                                              Pass      Fail      Pass    Pass                                     Stress                                                                        Crazing  Fail      Pass      Fail    Pass                                     Anti-Skid                                                                              3-4       6-8       7-8     7-8                                      Adhesion N/A       Pass      Fail    Pass                                     ______________________________________                                    

Although the above examples have shown various modifications of thepresent invention, other variations are possible in the light of theabove teachings. It is therefore to be understood that changes may bemade in the particular embodiments of the invention described which arewithin the full intended scope of the invention as defined by theappended claims.

What is claimed is:
 1. A coated polycarbonate article having a coatingthereon containing:(a) a polythiol represented by the general formula:##STR16## wherein R₁ and R₂ are organic moieties containing no reactivecarbon-to-carbon unsaturation and a is 2 to 4; (b) a polyene representedby the general formula: ##STR17## wherein R₃ and R₄ are organic moietiescontaining no reactive carbon-to-carbon unsaturation and b is 2 orgreater; and (c) a polyene represented by the general formula: ##STR18##wherein R₆ and R₇ are organic moieties containing no reactivecarbon-to-carbon unsaturation and c is 1 or greater, and wherein (a) and(b) plus (c) are used in stoichiometric amounts.
 2. The coatedpolycarbonate article of claim 1 in the form of a sheet.
 3. The coatedpolycarbonate article of claim 1 wherein the polythiol of (a) isrepresented by the following formula: ##STR19## wherein R₁ and R₂ arestraight chain aliphatic moieties containing no reactivecarbon-to-carbon unsaturation and a is 2 to
 4. 4. The coatedpolycarbonate article of claim 1 wherein the polyene of (b) is anoligomer of diallyl phthalate having residual unsaturation of the typerepresented by the general formula: ##STR20## wherein R₇ is an organicmoiety derived from diallyl phthalate by oligomerization and b is aninteger of 2 or greater.
 5. The coated polycarbonate article of claim 1wherein the polyene of (b) is represented by the formula: ##STR21## 6.The coated polycarbonate article of claim 1 wherein the polyene of (c)is represented by the formula: ##STR22## wherein R₆ and R₇ are organicmoieties containing no reactive carbon-to-carbon unsaturation.
 7. Thecoated polycarbonate article of claim 1 wherein the polyene of (c) isrepresented by the formula: ##STR23## wherein R₆ is an organic moietycontaining no reactive carbon-to-carbon unsaturation and has a molecularweight of about 1000.